Monitoring Dioxins

Dioxins, a family of 210 compounds of
which 17 are considered toxic and virtually nonbiodegradable, pose an
environmental hazard that may be watched even more closely with the advent of
technology being developed by Agricultural
Research Service scientists.

Produced by natural and industrial processes, dioxins are chlorinated aromatic
compounds that can build up in fatty tissue and may increase the risk of tumors
and possibly other undesirable health effects. Some forms, or congeners, of
dioxins are more toxic than others. One, known chemically as
2,3,7,8-tetrachlorodibenzo-p-dioxin, is so toxic that, according to U.S.
Environmental Protection Agency (EPA) standards, less than 0.1 milligram in a
water supply the size of an Olympic swimming pool is enough to render the water
unfit for drinking.

Water, however, is not a major source of dioxin exposure for humans. A more
usual source is our food supply, for example, food products from animals that
have eaten feed contaminated by the fat-soluble chemical, says chemist Janice
K. Huwe, lead scientist in dioxin research at the ARS Animal
Metabolism-Agricultural Chemicals Research Unit at Fargo, North Dakota.

Chemists Gerald Larsen (left) and Heldur Hakk
prepare to dose a rat for a metabolism study.(K9224-1)

A case in point: In 1997, USDA Food
Safety and Inspection Service inspectors sampled chicken meat being sold in
Mississippi and found it high in dioxins. The ARS scientists in Fargo, working
with EPA, helped uncover the extent of contamination and ferreted out the
source.

The researchers traced the dioxin to chicken feed, specifically soybean meal.
Ball clay, which is naturally contaminated by dioxins, had been used as a
desiccant, or drying material, to enhance the soybean meal's flowability during
processing. FDA has since recommended that clays used as desiccants in feed
processing be tested for dioxin.

More recently, high levels of dioxin showed up in some foods of animal origin
produced in Belgium. Food recalls and temporary international trade
restrictions followed. In this instance, the dioxin source was traced to
contaminated animal fats that had been added to chicken feed and other animal
feedstuffs.

Dioxins are in the family of chemicals called chlorinated hydrocarbons. From
time immemorial, they have been formed by wood combustion. In modern times,
their formation has come from garbage incinerated at temperatures below 1,800
°F, the manufacture and use of some herbicides, chlorine bleaching of wood
pulp and paper, and other industrial processes.

Given that these processes may release dioxins into the atmosphere, EPA also
began to consider, 7 years ago, the possible importance of air pollution in the
dioxin contamination of forage and other livestock feeds.

In a USDA fact-finding mission to investigate the extent of dioxin
contamination in livestock from all sources, the Fargo team researched dioxins
in beef. They collected and analyzed beef samples from 13 states, including
Hawaii. "By and large, we found the samples were clean, with some
outstanding exceptions in the kidney fat of some individual carcasses,"
says Huwe. Samples with high dioxin levels were found to have come from animals
raised in barns or pens containing posts that had been treated with
dioxin-containing pentachlorophenol (penta) to prevent rotting.

In laboratory studies, ARS scientists determine
what happens to dioxin compounds after they are fed to rats.(K9225-1)

Now, according to EPA regulations,
wood preservatives used for fence posts or feeding troughs in barns can no
longer contain penta. And penta sold in the United States for uses such as
preserving utility poles must now be manufactured under conditions that do not
produce 2,3,7,8-tetrachlorodibenzo-p-dioxin and that minimize the
concentration of another toxic congener,
1,2,3,6,7,8-hexachlorodibenzo-p-dioxin. No single batch of penta can
have levels higher than 4 parts per million (ppm), and the average
concentration among batches must not exceed 2 ppm.

Tracing Toxins

The scientists at Fargo are identifying routes of exposure and distribution of
the 17 toxic congeners in animals being raised for food and how this affects
our food supply. Pioneering research by ARS chemist Vernon J. Feil (retired)
and his colleagues on some of the less toxic congeners is helping to advance
studies on others.

After feeding different congeners of dioxins to laboratory and farm animals,
the scientists determine what happens to the molecules. For example, do the
dioxins end up in meat? And if so, are they converted to forms that are any
more or less dangerous to health than the original congeners?

In other research, ARS chemists Heldur Hakk and Gerald L. Larsen and animal
physiologist Nancy W. Shappell are exploring methods to minimize the burden of
dioxin compounds that persist in animals' bodies. These methods involve either
decreasing the amounts assimilated from feed or increasing the efficiency of
biochemical pathways to excrete them.

With new technologies, the scientists are now making headway in the
researchat lower costs. When research began, dioxin analysis cost nearly
$2,000 per sample. It's now down to about $600 to $800 per sample. Huwe and
chemist Weilin L. Shelver at Fargo are developing an even more efficient
procedurean immunoaffinity column methodwhich requires minimal use
of chemical solvents for the isolation of dioxins from foods. They expect
analysis costs with the new method will eventually drop to $300 or $400 per
sample. One of several antibodies used in the procedure was created through
research by ARS biologist Larry H. Stanker (formerly at College Station,
Texas).

The Food Safety and Inspection Service plans to resurvey beef, pork, and
chicken for dioxin contamination to get a better picture of the background
levels in the U.S. food supply.

Such knowledge came in handy last year when a beef sample exported to Japan had
high dioxin levels. It turned out that, in this isolated incident, the
particular congener involved was one of the least toxic. No further problems
have been found in shipments of U.S. beef to Japan.By
Ben Hardin,
Agricultural Research Service Information Staff.